Return exit code on command failure instead of throwing

[vijit-lark]

Summary

• Return exit code on command failure instead of throwing: Non-zero exit codes from command execution are now returned as part of the result instead of raising an error. When a command fails, remaining commands in the batch are skipped and only executed commands appear in the result message.
• Log warning on unexpected WebSocket disconnects: Adds finalized and cancelled flags to WebSocketSession so the close event handler can distinguish graceful shutdowns from unexpected client disconnects, and logs a warning with the WebSocket close code and reason.
• Add warn to Logger: Adds warn method to the Logger interface and all implementations (createLogger, createRedactingLogger, defaultLogger).
• Bumps both runtimeuse and runtimeuse-client to 0.10.0 (breaking: new required warn method on Logger, changed command failure behavior).

Test plan

• Run existing unit tests (npm test in packages/runtimeuse) to verify mock loggers and command failure behavior
• Manually test graceful shutdown path — should see "All artifacts uploaded." and no warning
• Manually test abrupt client disconnect — should see the new warning with close code/reason
• Manually test cancel flow — should see cancel log but no unexpected-close warning
• Verify failed command (exit 1) returns result with exit_code: 1 instead of throwing
• Verify remaining commands are skipped after a non-zero exit code
• Run Python client tests (uv run pytest in packages/runtimeuse-client-python)